From WILSONDO@phibred.com Mon Jun 21 11:14:52 1999
Date: Mon, 21 Jun 1999 04:49:39 -0500
From: "Wilson, Dale"
To: 'Russ Bulluck' ,
Sustainable Ag
Subject: RE: mildew question
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Russ,
> I apologise for the impromptu lecture on plant pathology,
> and thank you for your attention.
Don't apologize, plant pathology is very interesting.
> There are (as Dale points out) certain chemicals that
> cause plants to turn on these universal defenses (Actiguard,
> by Novartis, is one. Salicylic acid is another component,
It would be nice if organic growers could turn on systemic acquired
resistance (SAR) using non-synthetic chemicals. Can salicylic acid do this
in a practical sense?
> Mildews are just too specific.
Since SAR is a fairly generalized response, it might be possible to turn it
on in a plant using a non-specific, sub-virulent pathogenic assault. Are
their less fastidious pathogens that one could brew up and spray on to
trigger SAR, or would that be playing with fire? I am thinking of
facultative saprophytes that will germinate and "attempt" to infect almost
anything.
> The important thing to remember is that most plant pathogens
> don't cause plant disease on most plants. Disease is always
> the exception. Reactions to pathogens go from none to resistant
> reactions to susceptible reactions (disease).
Don't certain bacteria colonize the leaf surface? It is amazing to me how
seed-borne Xanthomonads and Pseudomonads can survive and propagate in plant
canopies, causing disease even under arid conditions. They must have a very
intimate relationship with the leaf surface. Of course, in the grand scheme
of things fungi are much more important pathogens Could fungal triggers of
SAR be put into leaf-surface bacteria to get generic SAR triggers?
Dale
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From lrbulluc@unity.ncsu.edu Mon Jun 21 11:16:28 1999
Date: Mon, 21 Jun 1999 09:10:16 -0400
From: Russ Bulluck
To: "Wilson, Dale"
Cc: Sustainable Ag
Subject: Re: mildew question
"Wilson, Dale" wrote:
> Russ,
>
> > I apologise for the impromptu lecture on plant pathology,
> > and thank you for your attention.
>
> Don't apologize, plant pathology is very interesting.
>
> > There are (as Dale points out) certain chemicals that
> > cause plants to turn on these universal defenses (Actiguard,
> > by Novartis, is one. Salicylic acid is another component,
>
> It would be nice if organic growers could turn on systemic acquired
> resistance (SAR) using non-synthetic chemicals. Can salicylic acid do this
> in a practical sense?
>
It would be nice. Salicylic acid is very difficult to get into plants, and I
don't think it is UV stable. It is a signalling molecule in the SAR pathway,
and can be found in the Xylem and intracellular matrix (I think).
Phosphoric acid (found in Coca Cola) is better at turning on the SAR. I think
that it is one of the major ingredients in Alloette (sp).
One problem with turning on the SAR pathway is that the plant devotes a _large_
amount of energy producing compounds to prevent infection, and not on fruit
production.
>
> > Mildews are just too specific.
>
> Since SAR is a fairly generalized response, it might be possible to turn it
> on in a plant using a non-specific, sub-virulent pathogenic assault. Are
> their less fastidious pathogens that one could brew up and spray on to
> trigger SAR, or would that be playing with fire? I am thinking of
> facultative saprophytes that will germinate and "attempt" to infect almost
> anything.
>
In theory, yes. Are you playing with fire? Yes. The best thing to do might be
to brew up a batch of _highly_ pathogenic bugs, and then boil the batch, and use
the extract to spray. The extract may contain materials that could induce SAR.
Of course, the extract could also contain heat-stabile enzymes that would kill
your plants! I would do this with fungi, but not bacteria, and with _great_
caution. Better yet, I would let a university experiment station do this, and
watch to see what happens to their fields!
>
> > The important thing to remember is that most plant pathogens
> > don't cause plant disease on most plants. Disease is always
> > the exception. Reactions to pathogens go from none to resistant
> > reactions to susceptible reactions (disease).
>
> Don't certain bacteria colonize the leaf surface? It is amazing to me how
> seed-borne Xanthomonads and Pseudomonads can survive and propagate in plant
> canopies, causing disease even under arid conditions. They must have a very
> intimate relationship with the leaf surface. Of course, in the grand scheme
> of things fungi are much more important pathogens Could fungal triggers of
> SAR be put into leaf-surface bacteria to get generic SAR triggers?
>
> Dale
Sorry, I didn't mention bacteria or nematodes (or viruses for that matter) .
Both of which can cause disease, and induce SAR (in fact the SAR phenomenon was
first observed in TMV infection and subsequent TMV challenging to different
leaves on the same plant).
Most plant pathogenic bacteria (except for most of the Erwinia spp.) do tend to
survive epiphitically, and will cause SAR to occur. Most often hypersensitive
responses occur (a different phenomenon all together), and are usually caused by
a direct genetic response. Once SAR is induced (by fungi, virus, herbivory, or
bacteria) it can be effective against all pathogens.
--
Russ Bulluck
Ph.D. Candidate
Department of Plant Pathology
North Carolina State University
PO Box 7616
Raleigh, NC 27695-7616
http://www.cals.ncsu.edu/plantpath/Personnel/Students/webpage.htm
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The soil population is so complex that it manifestly cannot
be dealt with as a whole with any detail by any one person,
and at the same time it plays so important a part in the soil
economy that it must be studied.
--Sir E. John Russell
The Micro-organisms of the Soil, 1923
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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From bluestem@webserf.net Mon Jun 21 11:18:14 1999
Date: Mon, 21 Jun 1999 13:06:16 +0100
From: Bluestem Associates
To: "sanet-mg@ces.ncsu.edu"
Subject: Mildew, etc.
Time to pop in with a brief observation from a soil chemist's point of
view.
You can accomplish a lot by way of increasing resistance to fungal
pathogens by making sure that the crop has abundant *available*
calcium. Calcium plays a key role in strengthening plant pectins, and
these pectins (in turn) often provide the most important barrier to the
polygalcturonase used by many (most???) fungi to exploit an infection
court when germinating.
Anyone who has ever made a low-sugar jam using low-methoxy pectin (e.g.
Pomona) has exploited this phenomenon to stiffen the pectin by adding
small amounts of soluble calcium.
There is also some benefit to be had from ensuring abundant manganese
availability to the crop. This can be tricky because at low pH Mn is
toxic, and in alkaline conditions is often unavailable. Manganese is
polyvalent with a vengence (largely pH dependent), but high levels of
the non-toxic forms will allow the plant to be somewhat more resistant
to attack.
Copper nutrition is also a potentially interesting element of plant
health, though the information is rather more anecdotal than in the
case of manganese. Increasing soil copper levels has been effective in
greatly reducing white mould damage to edible beans in some areas of
Michigan. Many Chilean grapes grow in high copper soils and rarely need
a fungicide treatment, in spite of significant pressure. Warrants
further study, in any case.
What is interesting to note (a bit sad, even) is the extent to which
the conventional research establishment has dismissed calcium,
manganese, and copper, almoste entirely because they *don't increase
yields.* We don't need *more* crops, we need HEALTHIER crops. It's
easier and more profitable to let the crops get sick and subsequently
treat them with something out of a bag.
Add to good nutrient management some of the newer fungal antagonists
(Trichoderma harzianum and some others) and you have the makings of a
reasonably sound preventative program. It all begins in the soil.
Bart Hall
Lawrence, Kansas
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"Wilson, Dale" wrote:
> Hi Russ,
>
> > Phosphoric acid (found in Coca Cola) is better at turning on
> > the SAR. I think that it is one of the major ingredients in
> > Alloette (sp).
>
> I believe it is salts of phosphorOUS acid (H3PO3) rather than PhosphorIC
> acid (H3PO4). This is confusing, since phosphorous acid is also called
> phosphonic acid. Rumor has it that spraying off-the-shelf phosphonate is
> almost as good as Aliette (aluminum ethyl phosphonate).
>
Okay, I'm not a chemist. But I suspect you are right. I'm under the
impression that Rhone-Poulenc has a "use-patent" on phosphonate. That you
can't legally just spray phosphonate. Not sure. . . just what I've heard. .
.Russ
--
Russ Bulluck
Ph.D. Candidate
Department of Plant Pathology
North Carolina State University
PO Box 7616
Raleigh, NC 27695-7616
http://www.cals.ncsu.edu/plantpath/Personnel/Students/webpage.htm
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The soil population is so complex that it manifestly cannot
be dealt with as a whole with any detail by any one person,
and at the same time it plays so important a part in the soil
economy that it must be studied.
--Sir E. John Russell
The Micro-organisms of the Soil, 1923
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~